Solar cell and solar cell module

ABSTRACT

In one or more embodiments, a solar cell may include: a silicon substrate, which is crystalline; a p-doped silicon oxide layer, which may be disposed on a first principal surface of the silicon substrate and may include phosphorus as an impurity; and an amorphous silicon layer, which may be disposed on the p-doped silicon oxide layer.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority from Japanese PatentApplication Number 2016-017417 filed on Feb. 1, 2016, the entirecontents of which are hereby incorporated herein by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to a solar cell and a solar cell module.

2. Description of the Related Art

Hybrid solar cells having a heterojunction structure of a crystallinesemiconductor substrate and an amorphous semiconductor thin film are inpractical use.

Patent Literature (PTL) 1 (Japanese Unexamined Patent ApplicationPublication No. 2003-324209) discloses a photovoltaic device whichimproves interface characteristics between a crystalline semiconductorsubstrate and an amorphous semiconductor thin film to improvephotoelectric conversion characteristics. Specifically, in thephotovoltaic device disclosed by PTL 1, a p-type amorphous silicon thinfilm is laminated above a first principal surface of an n-typesingle-crystal silicon substrate with a first i-type amorphous siliconthin film being between the n-type single-crystal silicon substrate andthe p-type amorphous silicon thin film. On the other hand, an n-typeamorphous silicon thin film is laminated above a second principalsurface of the n-type single-crystal silicon substrate with a secondi-type amorphous silicon thin film being between the n-typesingle-crystal silicon substrate and the n-type amorphous silicon thinfilm. In the above configuration, after the second principal surface ofthe single-crystal silicon substrate is plasma-treated by plasmadischarge using a mixed gas of a hydrogen gas and a gas includingphosphorus on the second principal surface of the single-crystal siliconsubstrate, the second i-type amorphous silicon layer is formed. Withthis, phosphorus is introduced into an interface between thesingle-crystal silicon substrate and the second i-type amorphous siliconlayer.

The above configuration makes it possible to reduce recombination ofcharge carriers in a semiconductor junction interface between thecrystalline semiconductor substrate and the amorphous semiconductor thinfilm, improve junction characteristics, and to improve the photoelectricconversion characteristics of open-circuit voltage (Voc) etc.

SUMMARY

In the above conventional photovoltaic device, introducing phosphorusinto the second principal surface of the n-type single-crystal siliconsubstrate causes defects in the second principal surface. These defectsin the second principal surface of the single-crystal silicon substratemake it impossible to completely reduce recombination of charge carriersin the second i-type amorphous silicon layer, and there is concern thatphotoelectric conversion characteristics are deteriorated.

In view of this, the present disclosure has been conceived to solve theabove problem, and an object of the present disclosure is to provide asolar cell having improved photoelectric conversion characteristics anda heterojunction structure, and a solar cell module.

In order to solve the above problem, a solar cell according to oneaspect of the present disclosure includes: a silicon substrate which iscrystalline; a first silicon oxide layer which is disposed on a firstprincipal surface of the silicon substrate and includes phosphorus as animpurity; and a first amorphous silicon layer disposed on the firstsilicon oxide layer.

The silicon oxide layer including phosphorus as the impurity is betweenthe silicon substrate which is crystalline and the amorphous siliconlayer in the solar cell or solar cell module according to one aspect ofthe present disclosure. Consequently, it is possible to provide thesolar cell with improved photoelectric conversion or the solar cellmodule with improved power generation efficiency.

BRIEF DESCRIPTION OF DRAWINGS

The figures depict one or more implementations in accordance with thepresent teaching, by way of examples only, not by way of limitations. Inthe figures, like reference numerals refer to the same or similarelements.

FIG. 1 is a diagram illustrating a schematic plan view of a solar cellmodule in accordance with one or more embodiments;

FIG. 2 is a diagram illustrating a structural cross-sectional view ofthe solar cell module in accordance with one or more embodiments, in acolumn direction;

FIG. 3 is a diagram illustrating a plan view of a solar cell inaccordance with one or more embodiments;

FIG. 4 is a diagram illustrating a schematic cross-sectional view of alaminated structure of the solar cell in accordance with one or moreembodiments;

FIG. 5 is a graph illustrating concentration profiles of oxygen andphosphorus with respect to a depth direction from a silicon substrate toan amorphous silicon layer; and

FIG. 6 is a diagram illustrating a schematic cross-sectional view of alaminated structure of a solar cell in accordance with variations of oneor more embodiments or alternative embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a solar cell and a solar cell module according to one ormore exemplary embodiments will be described in detail with reference tothe drawings. The exemplary embodiments described herein below aredirected to a specific example or examples. Therefore, numerical values,shapes, materials, structural components, the arrangement and connectionof the structural components, and steps, etc. described in the followingexemplary embodiments and shown in the figures are examples, and are notintended to limit the scope of the present disclosure. Accordingly, somestructural components may be described herein below in the followingexemplary embodiments, but may not be recited in any one of theindependent claims Such cases may be intended to indicate the broadestconcepts, and any structures omitted from the independent claims mayrefer to arbitrary structural components.

The respective figures are schematic diagrams and are not necessarilyprecise illustrations. In addition, in the respective figures, identicalstructural components are given the same reference signs.

In the present description, a “front surface” of a solar cell denotes asurface into which more light may enter inwardly in comparison to a“back surface” which is a surface opposite the front surface (at least50 to 100% of light enters inwardly from the front surface). Examples ofa front surface include a surface into which no light enters inwardlyfrom a “back surface” side. In addition, a “front surface” of a solarcell module denotes a surface into which light on a side opposite the“front surface” of the solar cell may enter, and a “back surface” of thesolar cell module denotes a surface opposite the front surface of thesolar cell module. Unless specifically otherwise limited, an expressionsuch as “provide a second member on a first member” is not intended torefer only to a condition in which the first and second members areprovided in direct contact with each other. In other words, theexpression “provide a second member on a first member” may refer to acondition in which another member is between the first and secondmembers. Moreover, the expression “substantially,” for example,“substantially the same” is intended to refer not only to a condition inwhich the described or recited quantities are exactly the same but alsoa condition where the recited quantities are not exactly the same butwould be recognized as being effectively the same.

1. Configuration of Solar Cell Module

An exemplary plane configuration of a solar cell module in accordancewith one or more embodiments will be described with reference to FIG. 1.

FIG. 1 is a diagram illustrating a schematic plan view of a solar cellmodule 100 in accordance with one or more embodiments. FIG. 2 is adiagram illustrating a structural cross-sectional view of the solar cellmodule 100 in accordance with one or more embodiments, in a columndirection. Specifically, FIG. 2 is a cross-sectional view of the sectionII-II of the solar cell module 100, e.g., as may be shown in FIG. 1.

As illustrated in FIG. 1, solar cell module 100 includes solar cells 1,tab lines 120, connecting lines 130, and a frame 150. In addition, asillustrated by FIG. 2, solar cell module 100 further includes a frontsurface encapsulant member 170 a, a back surface encapsulant member 170b, a front surface protective member 180 a, and a back surfaceprotective member 180 b.

The solar cells 1 are planar photovoltaic elements which may be arrangedin a matrix on a light-receiving surface and generate electric power inresponse to light irradiation.

Each of the tab lines 120 is a line member which is disposed on a frontsurface of each of the solar cells 1 and electrically connectsneighboring ones of the solar cells 1 in the column direction. The tabline 120 is a ribbon metal foil, for example. The tab line 120 may beproduced, for example, by cutting, into strips having a predeterminedlength, a metal foil such as a copper foil and a silver foil whoseentire surface is covered with solder, silver, etc.

Each of the connecting lines 130 is a line member connecting solar cellstrings. Each of the solar cell strings is an aggregate of cells of thesolar cells 1 arranged in the column direction and connected by tab line120.

The frame 150 is an outer frame member which covers an outer peripheryof a panel on which the solar cells 1 are two-dimensionally arrayed.

A light diffusion member may be disposed between neighboring ones of thesolar cells 1. The light diffusion member may cause light entering a gapregion between solar cells 1 to be redistributed to the solar cells 1,and thus light gathering efficiency of each of the solar cells 1 isincreased. Accordingly, it is possible to increase overall photoelectricconversion efficiency of the solar cell module.

As illustrated by FIG. 2, in which two cells of the solar cells 1neighbor each other in the column direction, the tab line 120 isdisposed on a front surface of one of two cells of the solar cells 1 isalso disposed on a back surface of the other of the two cells of thesolar cells 1. More specifically, a back surface at one end portion ofthe tab line 120 is bonded to a bus bar electrode on the front surfaceof the one of the two cells of the solar cells 1, and a front surface atthe other end portion of the table line 120 is bonded to a bus barelectrode on the back surface of the other of the two cells of the solarcells 1.

In an example, the tab line 120 and the bus bar electrode are bondedwith an electrically conductive adhesive. Examples of the electricallyconductive adhesive may include a conductive adhesive paste, aconductive adhesive film, and an anisotropic conductive film. In furtherexamples, the electrically adhesive paste may be a paste adhesiveproduced by dispersing conductive particles into a thermosettingadhesive resin material such as an epoxy resin, an acryl resin, and aurethane resin. Each of the electrically conductive adhesive film andthe anisotropic conductive film may be a film adhesive produced bydispersing conductive particles into a thermosetting adhesive resinmaterial.

The aforementioned electrically conductive adhesive may be a soldermaterial. Alternatively, or in addition, a resin adhesive including noconductive particles may be used instead of the electrically conductiveadhesive. In a condition in which no conductive particles are used, anapplication thickness for the resin adhesive should be suitably selectedto allow the resin adhesive to soften when pressure is applied at thetime of thermal compression bonding, such that the bus bar electrode andthe tab line 120 may be electrically connected in direct contact witheach other.

Moreover, as illustrated in FIG. 2, the front surface protective member180 a is provided on a front surface side of each of the cells of thesolar cells 1, and the back surface protective member 180 b is providedon a back surface side of each of the cells of the solar cells 1. Thefront surface encapsulant member 170 a is disposed between a surfaceincluding the cells of the solar cells 1 and the front surfaceprotective member 180 a, and the back surface encapsulant member 170 bis disposed between a surface including the cells of the solar cells 1and the back surface protective member 180 b. The front surfaceprotective member 180 a and the back surface protective member 180 b arefixed by the front surface encapsulant member 170 a and the back surfaceencapsulant member 170 b, respectively.

The front surface protective member 180 a is a translucent substratewhich protects a front surface side of the solar cell module 100, andprotects the inside (cells of the solar cells 1 etc.) of the solar cellmodule 100 from an external environment such as wind and rain, externalshock, and fire. The front surface protective member 180 a is atranslucent member having translucency, and is a glass substrate(transparent glass substrate) including a transparent glass material ora resin substrate including a film-like or plate-like hard resinmaterial having translucency and impermeability, for example.

The back surface protective member 180 b is a member which protects aback surface of the solar cell module 100 and includes, for example, aresin film such as polyethylene terephthalate or a laminated film havinga structure in which an Al foil is disposed between resin films.

The front surface encapsulant member 170 a and the back surfaceencapsulant member 170 b have a sealing function for isolating the cellsof the solar cells 1 from the external environment. Disposing the frontsurface encapsulant member 170 a and the back surface encapsulant member170 b in a sealing capacity makes it possible to ensure high heatresistance and high humidity resistance when the solar cell module 100is to be installed outdoors.

Each of the front surface encapsulant member 170 a and the back surfaceencapsulant member 170 b includes a translucent polymer material havinga sealing function. Examples of the polymer material of the frontsurface encapsulant member 170 a include a translucent resin materialsuch as ethylene-vinyl acetate (EVA).

In order to simplify a manufacturing process and to promote interfaceadherence between the front surface encapsulant member 170 a and theback surface encapsulant member 170 b, the front surface encapsulantmember 170 a and the back surface encapsulant member 170 b may includethe same material.

2. Structure of Solar Cell

The following describes a structure of each solar cell 1 of the solarcells 1, which is a main component of the solar cell module 100.

FIG. 3 is diagram illustrating a plan view of the solar cell 1 inaccordance with one or more embodiments. As illustrated by the figure,the solar cell 1 may be substantially square in a plan view. In oneexample, the solar cell 1 has a size of 125 mm in length×125 mm inwidth×200 μm in thickness. Moreover, on a surface of the solar cell 1,the bus bar electrodes 42 having a stripe shape are formed in parallelto each other, and the finger electrodes 41 having a stripe shape areformed in parallel to each other to cross the bus bar electrodes 42 atright angles. The bus bar electrodes 42 and the finger electrodes 41constitute a collector electrode 43. The collector electrode 43 isformed using, for example, a conductive paste including conductiveparticles such as Ag (silver). In an example, a line width of the busbar electrodes 42 is 1.5 mm, a line width of the finger electrodes 41 is100 μm, and a pitch of the finger electrodes 41 is 2 mm. Furthermore,the tab lines 120 are bonded onto the bus bar electrodes 42.

FIG. 4 is a diagram illustrating a schematic cross-sectional view of alaminated structure of the solar cell 1 in accordance with one or moreembodiments. FIG. 4 is a cross-sectional view of section IV-IV of thesolar cell 1, e.g., as may be shown in FIG. 3. As illustrated in FIG. 4,the solar cell 1 may include a silicon substrate 10, a p-doped siliconoxide layer 20, amorphous silicon layers 30 and 60, transparentelectrodes 40 and 70, and finger electrodes 41 and 71. For brevity, FIG.4 illustrates only finger electrode 41 included in the collectorelectrode 43.

The silicon substrate 10 is an n-type single-crystal silicon substratehaving a first principal surface and a second principal surface that arein back-to-back relation with each other. The silicon substrate 10 mayinclude polysilicon. Moreover, each of the first principal surface andthe second principal surface may have a textured structure in whichpyramids are two-dimensionally arranged. Furthermore, the siliconsubstrate 10 has an n-type dopant concentration of at least 3×10¹⁴/cm³and at most 9.1×10¹⁵/cm³, for example, and a resistivity of at least 0.5Ωcm and at most 15 Ωcm, for example. In addition, the silicon substrate10 has an n-type dopant concentration of at most 3×10¹⁵/cm³, and aresistivity of at least 1.5 Ωcm in order to further reduce therecombination of charge carriers. Additionally, in order to reduceoutput loss caused by series resistance, silicon substrate 10 has ann-type dopant concentration of at least 3.5×10¹⁴/cm³, and a resistivityof at most 13 Ωcm.

The p-doped silicon oxide layer 20 is a first silicon oxide layerdisposed on the first principal surface of the silicon substrate 10, andincludes a silicon oxide film including phosphorus as an impurity. In anexample, the p-doped silicon oxide layer 20 has a thickness of at least0.1 nm and at most 3 nm. The p-doped silicon oxide layer 20 may furtherhave a thickness of at most 2 nm. The p-doped silicon oxide layer 20 isthinner than a dielectric layer 31 and an n-type amorphous silicon layer32, to be described in greater detail hereafter. In addition, thep-doped silicon oxide layer 20 may be formed into an island shape, in aninterface between the silicon substrate 10 and the amorphous siliconlayer 30.

The p-doped silicon oxide layer 20 has a phosphorus concentration of atleast 1×10¹⁹/cm³ and at most 5×10²⁰/cm³, and an oxygen atomicconcentration of at least 1×10²¹/cm³ and at most 2×10²²/cm³. The p-dopedsilicon oxide layer 20 more preferably has a phosphorus concentration ofat least 5×10¹⁹/cm³ and at most 1×10²⁰/cm³, and an oxygen atomicconcentration of at least 2×10²¹/cm³ and at most 5×10²¹/cm³. The p-dopedsilicon oxide layer 20 may be an amorphous layer. In such an example,the p-doped silicon oxide layer 20 may be formed at low temperature ofat most 200° C.

The amorphous silicon layer 30 is a first amorphous silicon layer whichis formed on a front surface of the p-doped silicon oxide layer 20 andis in a substantially amorphous state. The amorphous silicon layer 30includes dielectric layer 31 and n-type amorphous silicon layer 32.

The dielectric layer 31 is a first dielectric layer formed on the frontsurface of p-doped silicon oxide layer 20. In an example, the dielectriclayer 31 a first intrinsic amorphous silicon layer that includeshydrogen and is in the amorphous state. In the present example, anintrinsic amorphous silicon layer denotes an amorphous semiconductorlayer having an included p-type or n-type dopant concentration of atmost 5×10¹⁸/cm³ or an amorphous semiconductor layer having, in a casewhere both p-type and n-type dopants are included, a difference betweena p-type dopant concentration and an n-type dopant concentration, whichis at most 5×10¹⁸/cm³. The dielectric layer 31 may be made sufficientlythin so as to reduce, as much as possible, the absorption of light. Atthe same time, the dielectric layer 31 may be made sufficiently thick soas to sufficiently passivate a front surface of silicon substrate 10. Inan example, the dielectric layer 31 has a film thickness of at least 1nm and at most 25 nm. Alternatively, the dielectric layer 31 has a filmthickness of at least 5 nm and at most 10 nm.

In some embodiments, the dielectric layer 31 may not be the intrinsicamorphous silicon layer as described above, and may be a silicon oxidelayer, a silicon nitride layer, or an aluminum oxide layer. Moreover,the dielectric layer 31 may not be present, and the n-type amorphoussilicon layer 32 may be directly formed on the front surface of thep-doped silicon oxide layer 20.

The n-type amorphous silicon layer 32 is a first conductive amorphoussilicon layer which is formed on the dielectric layer 31. The n-typeamorphous silicon layer 32 includes n-type dopants of a sameconductivity type as the silicon substrate 10, and is in a substantiallyamorphous state. In an example, the n-type amorphous silicon layer 32includes an amorphous silicon semiconductor thin film includinghydrogen. The n-type amorphous silicon layer 32 has a higher n-typedopant concentration in a film than the dielectric layer 31, and has ann-type dopant concentration of at least 1×10²⁰/cm³. Examples of n-typedopants may include phosphorus (P). The n-type amorphous silicon layer32 may be made sufficiently thin to reduce, as much as possible, theabsorption of light. At the same time the n-type amorphous silicon layer32 may be made sufficiently thick to effectively separate chargecarriers generated in the silicon substrate 10 and to allow thetransparent electrode 40 to efficiently collect the generated chargecarriers. The n-type amorphous silicon layer 32 has an n-type dopantconcentration that may gradually change concentration from a side of thep-doped silicon oxide layer 20 to a side of the transparent electrode40.

The amorphous silicon layer 60 is a second amorphous silicon layer whichis disposed on the second principal surface of silicon substrate 10 andis in a substantially amorphous state. The amorphous silicon layer 60includes a dielectric layer 61 and a p-type amorphous silicon layer 62.

The dielectric layer 61 is a second dielectric layer formed on thesecond principal surface of the silicon substrate 10. In an example, thedielectric layer 61 is a second intrinsic amorphous silicon layer thatincludes hydrogen and is in an amorphous state. In an example, thedielectric layer 61, like the dielectric layer 31, has a film thicknessof at least 1 nm and at most 25 nm. Alternatively, the dielectric layer31 has a film thickness of at least 5 nm and at most 10 nm.

In some embodiments, the dielectric layer 61 may not be an intrinsicamorphous silicon layer as described above, and may be a silicon oxidelayer, a silicon nitride layer, or an aluminum oxide layer.Alternatively or in addition, the dielectric layer 61 may not bepresent, and the p-type amorphous silicon layer 62 may be directlyformed on the second principal surface of the silicon substrate 10.

The p-type amorphous silicon layer 62 is a second conductive amorphoussilicon layer which is formed on the dielectric layer 61, includesp-type dopants, which is an opposite conductivity type of the siliconsubstrate 10, and is substantially in the amorphous state. The p-typeamorphous silicon layer 62 includes, for example, an amorphous siliconsemiconductor thin film including hydrogen. The p-type amorphous siliconlayer 62 has a higher p-type dopant concentration in a film than thedielectric layer 61, and preferably has a p-type dopant concentration ofat least 1×10²⁰/cm³. Examples of p-type dopants may include boron (B).The p-type amorphous silicon layer 62 may be made sufficiently thin toreduce, as much as possible, the absorption of light. At the same time,the p-type amorphous silicon layer 62 may be made sufficiently thick toeffectively separate charge carriers generated in the silicon substrate10 and to allow the transparent electrode 70 to efficiently collect thegenerated charge carriers. The p-type amorphous silicon layer 62 has ap-type dopant concentration that may gradually change from a side of thesilicon substrate 10 to a side of the transparent electrode 70.

Each of the amorphous silicon layer 30, the amorphous silicon layer 60,the n-type amorphous silicon layer 32, and the p-type amorphous siliconlayer 62 may include a microcrystal.

The transparent electrode 40 is formed on a front surface of amorphoussilicon layer 30, and collects charge carriers in the n-type amorphoussilicon layer 32. Moreover, the transparent electrode 70 is formed on aback surface of the amorphous silicon layer 60, and collects chargecarriers in the p-type amorphous silicon layer 62. In an example, eachof the transparent electrodes 40 and 70 may include a transparentconductive oxide such as indium tin oxide (ITO).

In some embodiments, determining which of the first principal surfaceand the second principal surface of silicon substrate 10 is used as alight-receiving surface (surface which mainly introduces light from theoutside) is optional.

Moreover, although the conductivity type of the silicon substrate 10 hasbeen described as having the n-type in one or more embodiments, in someembodiments, the conductivity type of the silicon substrate 10 may bethe p-type. In such an example, in a condition in which the siliconsubstrate 10 is of a p-type, the p-type amorphous silicon layer 62 ofthe amorphous silicon layer 60 has the same conductivity type as theconductivity type of the silicon substrate 10. Thus, the amorphoussilicon layer 60 is the first amorphous silicon layer. In addition, then-type amorphous silicon layer 32 of the amorphous silicon layer 30 hasa conductivity type opposite of the conductivity type of the siliconsubstrate 10, and thus the amorphous silicon layer 30 is the secondamorphous silicon layer.

Moreover, although the solar cell 1 in accordance with one or moreembodiments has been described as a bifacial solar cell including thetransparent electrode 70 disposed also on a side of a second principalsurface, the solar cell 1 may be a unifacial solar cell including,instead of the transparent electrode 70, a metal electrode that is nottransparent.

FIG. 5 is a graph illustrating concentration profiles of oxygen andphosphorus with respect to a depth direction from the amorphous siliconlayer 30 to the silicon substrate 10. In the graph of FIG. 5,concentrations of oxygen and phosphorus are measured by secondary ionmass spectroscopy (SIMS) in a direction (depth direction) from theamorphous silicon layer 30 to the silicon substrate 10. Reviewing thegraph of FIG. 5 reveals that absolute maximum points of an oxygen atomicconcentration and a phosphorus atomic concentration are present in thedepth direction and are located at the same depth. FIG. 5 furtherreveals that the oxygen atomic concentration is higher than thephosphorus atomic concentration by at least one order of magnitude atthe maxima. Accordingly, the illustrated characteristics are producedaccording to a silicon oxide layer including phosphorus as an impurity(p-doped silicon oxide layer 20) between amorphous silicon layer 30 andsilicon substrate 10. As may be obvious from a review of the graph inFIG. 5, the p-doped silicon oxide layer 20 has an atomic concentrationof phosphorus of at least 1×10¹⁹/cm³ and at most 5×10²⁰/cm³, and anatomic concentration of oxygen of at least 1×10²¹/cm³ and at most2×10²²/cm³.

In a conventional photoelectric conversion device, setting an impurityconcentration of a silicon substrate in a heterojunction between acrystalline silicon substrate and an amorphous silicon layer to be apredetermined amount makes it possible to reduce recombination of chargecarriers in a junction interface. As a result of the conventionalimpurity concentration setting, improvement an open-circuit voltage(Voc) is expected. However, the introduction of an impurity (e.g.,phosphorus) into a front surface of the silicon substrate causes defectsin the front surface, which make it impossible to completely reducerecombination of charge carriers in the amorphous silicon layer.Moreover, by increasing the impurity concentration of a siliconsubstrate to further improve photoelectric conversion characteristics, areduction in an electric field strength of the amorphous silicon layermay be achieved. Consequently, the recombination of the charge carriersin the amorphous silicon layer is increased. Furthermore, recombinationmay be accelerated via the introduction of excessive impurities in theamorphous silicon layer. In other words, introducing an impurity intothe front surface of the silicon substrate only cannot completely reducethe recombination of the charge carriers in the amorphous silicon layer.In addition, an excessive concentration of impurities in the frontsurface of the silicon substrate increases the defects in the frontsurface of the silicon substrate, and thus deteriorates thephotoelectric conversion characteristics.

In contrast, with the solar cell 1 in accordance with one or moreembodiments, a silicon oxide layer is disposed between amorphous siliconlayer 30 and silicon substrate 10, and the silicon dioxide layer isdoped with phosphorus. Stated differently, the p-doped silicon oxidelayer 20 including phosphorus as the impurity is disposed betweenamorphous silicon layer 30 and silicon substrate 10.

In order to improve an open-circuit voltage, it may be advantageous tomaintain a high degree of amorphousness of the amorphous silicon layer30 in addition to reducing recombination of charge carriers caused byimpurity doping. From this perspective, disposing a silicon oxide layerbetween the amorphous silicon layer 30 and the silicon substrate 10makes it possible to suppress, in the amorphous silicon layer 30,epitaxial growth reflecting crystallinity of the silicon substrate 10.Moreover, in a condition in which, instead of an impurity, the p-dopedsilicon oxide layer 20 is disposed in the junction interface, it becomespossible to reduce the increasing of the defects in the front surface ofthe silicon substrate 10 and to thereby improve the open-circuitvoltage.

In sum, with the solar cell 1 in accordance with one or moreembodiments, disposing the silicon oxide layer including phosphorus asthe impurity between the amorphous silicon layer 30 and the siliconsubstrate 10 makes it possible to reduce the recombination of the chargecarriers in the interface and suppress the epitaxial growth in theamorphous silicon layer 30. Accordingly, since it is possible toameliorate field effect, an improvement in the open-circuit voltage,which is not possible from merely doping impurities into the siliconsubstrate, can be achieved. Alternatively or in addition, it is possibleto improve the open-circuit voltage without degrading the photoelectricconversion performance that depends on the defects in the front surfaceof the silicon substrate.

3. Structure of Solar Cell According to Variation

FIG. 6 is a diagram illustrating a schematic cross-sectional view of alaminated structure of a solar cell 1 a in accordance with a variationof one or more embodiments. As illustrated in FIG. 6, the solar cell 1 adiffers from the solar cell 1 in accordance with one or more embodimentsin that diffusion region 10 a of phosphorus is in a front surface (firstprincipal surface) of the silicon substrate 10. In other words, in solarcell 1 a according to a variation, the silicon substrate 10 has, in thefirst principal surface, the diffusion region 10 a including phosphorusas an impurity. In this regard, however, the diffusion region 10 a has aphosphorus atomic concentration lower than a phosphorus atomicconcentration of the p-doped silicon oxide layer 20. Moreover, in anexample, the diffusion region 10 a may have an atomic concentration ofphosphorus of at least 5×10¹⁶/cm³ and at most 5×10²⁰/cm³, which ishigher than an n-type dopant concentration of the silicon substrate 10.Furthermore, in an example, a depth of the diffusion region 10 a fromthe front surface of silicon substrate 10 is at most 1.5 μm. In theexample configuration, the p-doped silicon oxide layer 20 is between theamorphous silicon layer 30 and the silicon substrate 10. Thus, it ispossible to reduce recombination of charge carriers on a side of thefirst principal surface of the silicon substrate 10 and to suppressepitaxial growth in the amorphous silicon layer 30. Accordingly, animprovement in the open-circuit voltage may be achieved. In thedescribed example, a diffusion region of phosphorus may be in a secondprincipal surface of the silicon substrate 10.

In addition, the diffusion region in a variation is not limited to aregion formed using a thermal diffusion method. Examples of methods offormation of the diffusion region in the variation may include formingthe diffusion region using a plasma doping method, an epitaxial growthmethod, an ion implantation method, or other methods.

4. Method for Manufacturing Solar Cell

Next, a method for manufacturing the solar cell 1 including thecharacteristics of the above described p-doped silicon oxide layer 20,will be described.

First, the silicon substrate 10 is washed, placed in a vacuum chamber,and heated to at most 200° C. to remove, as much as possible, moistureon a front surface of the silicon substrate 10.

Next, a hydrogen gas is introduced into the vacuum chamber, and thefront surface of the silicon substrate 10 is cleaned by plasmadischarge. The plasma discharge cleaning process has an additionaleffect of reducing an amount of carbon of the surface of the siliconsubstrate 10.

Next, the p-doped silicon oxide layer 20, the dielectric layer 31 (firstintrinsic amorphous silicon layer), and the n-type amorphous siliconlayer 32 are sequentially formed on the first principal surface of thesilicon substrate 10. In an example, layers are formed on the firstprincipal surface of the silicon substrate 10 after a front surfacethereof has been cleaned, by chemical vapor deposition (CVD). Thep-doped silicon oxide layer 20 is formed by introducing, into a vacuumdeposition chamber, a silicon-containing gas such as silane (SiH₄), ann-type dopant-containing gas such as phosphine (PH₃), and anoxygen-containing gas such as O₂, H₂O, and CO₂, for example. Thedielectric layer 31 (first intrinsic amorphous silicon layer) is formedby introducing, into the vacuum deposition chamber, thesilicon-containing gas such as silane (SiH₄). The n-type amorphoussilicon layer 32 is formed by introducing, into the vacuum depositionchamber, a silane (SiH₄) gas and the n-type dopant-containing gas suchas phosphine (PH₃).

Next, the dielectric layer 61 (second intrinsic amorphous silicon layer)and the p-type amorphous silicon layer 62 are sequentially formed on thesecond principal surface of the silicon substrate 10. In an example, thelayers may be formed by CVD. The dielectric layer 61 (second intrinsicamorphous silicon layer) is formed by introducing, into the vacuumdeposition chamber, the silicon-containing gas such as silane (SiH₄)gas. The p-type amorphous silicon layer 62 is formed by introducing,into the vacuum deposition chamber, silane (SiH₄) gas and a p-typedopant-containing gas such as diborane (B₂H₆).

In some examples, the gases introduced in each of the manufacturingsteps may be gases diluted with hydrogen gas, or other gas suitable fordilution.

Through the above steps, the p-doped silicon oxide layer 20 and theamorphous silicon layer 30 are formed on the first principal surface ofthe silicon substrate 10, and the amorphous silicon layer 60 is formedon the second principal surface of the silicon substrate 10.

Next, the transparent electrode 40 is formed on a front surface of theamorphous silicon layer 30, and the transparent electrode 70 is formedon a back surface of the amorphous silicon layer 60. Specifically, atransparent conductive oxide such as indium tin oxide (ITO) is depositedas a film on each of a front surface of the n-type amorphous siliconlayer 32 and a back surface of the p-type amorphous silicon layer 62 byvapor deposition, sputtering, etc.

Finally, the collector electrode 43 (metal electrode) including thefinger electrodes 41 is formed on the transparent electrode 40, and acollector electrode (metal electrode) including the finger electrodes 71is formed on transparent electrode 70. In an example, the collectorelectrodes may be formed by a printing method such as a screen printingmethod with a thermosetting resin conductive paste using a resinmaterial as a binder and conductive particles such as silver particlesas a filler.

Thus, the solar cell 1 in accordance with one or more embodiments may beformed through the above steps.

In the aforementioned method for manufacturing the solar cell 1, thesilicon substrate 10 may again be washed and cleaned by plasma dischargeafter the n-type amorphous silicon layer 32 is formed and before thedielectric layer 61 is formed.

Moreover, a textured structure having pyramids two-dimensionallyarranged, may be previously formed in at least one of the firstprincipal surface and the second principal surface of the siliconsubstrate 10. Specifically, the silicon substrate 10 is soaked in anetching solution. In an example, the etching solution is an alkalineaqueous solution including at least one of sodium hydroxide (NaOH),potassium hydroxide (KOH), and tetramethyl ammonium hydroxide (TMAH). Inan example, the first principal surface and the second principal surfaceof the silicon substrate 10 are anisotropically etched along a (111)plane by soaking a (100) plane of the silicon substrate 10 in the abovealkaline aqueous solution. As a result, a textured structure in whichsquare pyramids are two-dimensionally arranged is formed in each of thefirst principal surface and the second principal surface of the siliconsubstrate 10.

Forming ridges and troughs referred to as the textured structure inwhich the pyramids are two-dimensionally arranged in the light-receivingsurface of the solar cell 1 makes it possible to increase light enteringinside the solar cell 1 by reducing reflected light and to raise powergeneration efficiency of the solar cell 1.

5. Advantageous Effects Etc.

The solar cell 1 in accordance with one or more embodiments includes:the silicon substrate 10 which is crystalline and has a firstconductivity type (n-type); the p-doped silicon oxide layer 20, which isdisposed on the first principal surface of the silicon substrate 10, andincludes phosphorus as the impurity; and the amorphous silicon layer 30disposed on p-doped silicon oxide layer 20.

With a conventional photoelectric conversion device, setting an impurityconcentration of a silicon substrate in a heterojunction between acrystalline silicon substrate and an amorphous silicon layer to be apredetermined amount makes it possible to reduce recombination of chargecarriers in a junction interface. As a result, an improvement in anopen-circuit voltage (Voc) is expected. However, the introduction of animpurity (phosphorus) into a front surface of the silicon substratecauses defects in the front surface, which make it impossible tocompletely reduce recombination of charge carriers in the amorphoussilicon layer. Moreover, by increasing the impurity concentration of thesilicon substrate to further improve photoelectric conversioncharacteristics, a reduction in an electric field strength of theamorphous silicon layer may result. Consequently, the recombination ofthe charge carriers in the amorphous silicon layer is increased.Furthermore, recombination may be accelerated via introduction of theexcessive impurities in the amorphous silicon layer. In other words,introducing an impurity into the front surface of the silicon substrateonly cannot completely reduce the recombination of the charge carriersin the amorphous silicon layer. In addition, an excessive concentrationof impurities in the front surface of the silicon substrate increasesthe defects in the front surface of the silicon substrate, and thusdeteriorates the photoelectric conversion characteristics.

In contrast, with the solar cell 1 in accordance with one or moreembodiments, a silicon oxide layer is disposed between amorphous siliconlayer 30 and silicon substrate 10, and the silicon oxide layer includesphosphorus. Stated differently, the p-doped silicon oxide layer 20including phosphorus as an impurity is disposed between the amorphoussilicon layer 30 and the silicon substrate 10.

In order to improve an open-circuit voltage (Voc) of the solar cell 1,it may be advantageous to maintain a high degree of amorphousness of theamorphous silicon layer 30. From this perspective, disposing the siliconoxide layer 20 between the amorphous silicon layer 30 and the siliconsubstrate 10 makes it possible to suppress, in the amorphous siliconlayer 30, epitaxial growth reflecting crystallinity of the siliconsubstrate 10. Moreover, the p-doped silicon oxide layer 20 is disposedtherebetween, and thus it is possible to reduce the increasing of thedefects in the front surface of the silicon substrate 10, making it alsopossible to improve the open-circuit voltage.

In sum, with the solar cell 1 in accordance with one or moreembodiments, disposing the p-doped silicon oxide layer 20 between theamorphous silicon layer 30 and the silicon substrate 10 makes itpossible to reduce the recombination of the charge carriers in theinterface and suppress the epitaxial growth in the amorphous siliconlayer 30. Accordingly, the improvement of the open-circuit voltage whichcannot be achieved by merely doping impurity elements into the siliconsubstrate 10 can be achieved, or it is possible to improve theopen-circuit voltage without degrading photoelectric conversionperformance which depends on the defects in the front surface of thesilicon substrate 10.

Moreover, the amorphous silicon layer 30 may include: the dielectriclayer 31 (first intrinsic amorphous silicon layer) which issubstantially intrinsic and disposed on the front surface of the p-dopedsilicon oxide layer 20; and the n-type amorphous silicon layer 32 whichis disposed on a front surface of the dielectric layer 31 and includes afirst conductivity type (n-type) dopant.

With this, the dielectric layer 31 (first intrinsic amorphous siliconlayer) is between the silicon substrate 10 and the n-type amorphoussilicon layer 32. As a result, the recombination of the charge carriersin the junction interface may be reduced, which makes it possible topromote movement of the charge carriers.

Furthermore, in the p-doped silicon oxide layer 20, a phosphorus atomicconcentration may be at least 1×10¹⁹/cm³ and at most 5×10²⁰/cm³, and anoxygen atomic concentration may be at least 1×10²¹/cm³ and at most2×10²²/cm³.

In addition, in the p-doped silicon oxide layer 20, the atomicconcentration of phosphorus may be at least 5×10¹⁹/cm³ and at most1×10²⁰/cm³, and the atomic concentration of oxygen may be at least2×10²¹/cm³ and at most 5×10²¹/cm³.

Since the atomic concentration of oxygen is higher than the atomicconcentration of phosphorus, the p-doped silicon oxide layer 20 has astructure in which phosphorus is doped to the silicon oxide as theimpurity. With this, it is possible to reduce the recombination of thecharge carriers in the above interface and suppress the epitaxial growthin the amorphous silicon layer 30. Accordingly, the improvement of thephotoelectric conversion characteristics which cannot be achieved bymerely doping impurity elements into the silicon substrate 10 can beachieved, or it is possible to improve the open-circuit voltage withoutdegrading photoelectric conversion performance which depends on thedefects in the front surface of the silicon substrate 10.

Moreover, the silicon substrate 10 may include, in the first principalsurface, the diffusion region 10 a having a higher phosphorus atomicconcentration than the silicon substrate 10.

Even with this configuration, the p-doped silicon oxide layer 20 isbetween the amorphous silicon layer 30 and the silicon substrate 10, andthus it is possible to reduce the recombination of the charge carrierson the side of the first principal surface of the silicon substrate 10and suppress the epitaxial growth in the amorphous silicon layer 30.Accordingly, it is possible to achieve an improvement of theopen-circuit voltage.

Moreover, the solar cell 1 may further include the amorphous siliconlayer 60 which is disposed on a second principal surface which is backto back with the first principal surface of the silicon substrate 10.

Furthermore, the amorphous silicon layer 60 may include: the dielectriclayer 61 (second intrinsic amorphous silicon layer) which issubstantially intrinsic and disposed on the second principal surface ofthe silicon substrate 10; and the p-type amorphous silicon layer 62which is disposed on a back surface of the dielectric layer 61 andincludes a dopant of a second conductivity type (p-type).

The dielectric layer 61 (second intrinsic amorphous silicon layer) isbetween the silicon substrate 10 and the p-type amorphous silicon layer62. As a result, the recombination of the charge carriers in thejunction interface may be reduced, which makes it possible to promotemovement of the charge carriers.

Moreover, the solar cell module 100 in accordance with one or moreembodiments includes: a plurality of cells of the solar cells 1 whichare two-dimensionally arranged; the front surface protective member 180a disposed on a front surface side of the cells of the solar cells 1;back surface protective member 180 b disposed on a back surface side ofthe cells of the solar cells 1; the front surface encapsulant member 170a disposed between the cells of the solar cells 1 and the front surfaceprotective member 180 a; and the back surface encapsulant member 170 bdisposed between the cells of the solar cells 1 and the back surfaceprotective member 180 b.

With this, it is possible to reduce the recombination of the chargecarriers in the semiconductor junction interface between the siliconsubstrate 10 which is crystalline and the amorphous silicon layer 30,and to suppress the epitaxial growth in the amorphous silicon layer 30.Thus, the open-circuit voltage of the cells of the solar cells 1 may beimproved, which makes it possible to raise the power generationefficiency of the solar cell module 100.

Other Embodiments

Although solar cell 1 and solar cell module 100 according to the presentdisclosure have been described above based on the aforementioned one ormore embodiments, the present disclosure is not limited to theaforementioned one or embodiments.

For example, although, in the solar cell module 100 according to theaforementioned one or more embodiments, the cells of the solar cells 1are arranged in a matrix, the arrangement is not limited to a matrix.For example, the arrangement may be circular, linear, or curvilinear.

While the foregoing has described one or more embodiments and/or otherexamples, it is understood that various modifications may be madetherein and that the subject matter disclosed herein may be implementedin various forms and examples, and that they may be applied in numerousapplications, only some of which have been described herein. It isintended by the following claims to claim any and all modifications andvariations that fall within the true scope of the present teachings.

1-8. (canceled)
 9. A solar cell comprising: a crystalline siliconsubstrate; a first silicon oxide layer disposed on a first principalsurface of the crystalline silicon substrate and including phosphorus asan impurity; a first dielectric layer disposed on the first siliconoxide layer; a first conductivity type amorphous silicon layer disposedon the first dielectric layer and including a dopant of a firstconductivity type; a second dielectric layer disposed on a secondprincipal surface of the crystalline silicon substrate; and a secondconductivity type amorphous silicon layer disposed on the seconddielectric layer and including a dopant of a second conductivity type.10. The solar cell according to claim 9, wherein the first dielectriclayer comprises a first intrinsic dielectric layer being substantiallyintrinsic.
 11. The solar cell according to claim 9, wherein the firstdielectric layer comprises one of a silicon oxide layer, a siliconnitride layer, and an aluminum oxide layer.
 12. The solar cell accordingto claim 9, wherein the first conductivity type amorphous silicon layercomprises a microcrystal.
 13. The solar cell according to claim 9,wherein the crystalline silicon substrate comprises, in the firstprincipal surface, a diffusion region having a phosphorus concentrationhigher than that of the crystalline silicon substrate.
 14. The solarcell according to claim 13, wherein the phosphorus concentration of thediffusion region is lower than that of the first silicon oxide layer.15. The solar cell according to claim 9, wherein a concentration profileof phosphorus in a depth direction from the first conductivity typeamorphous silicon layer to the crystalline silicon substrate has amaximum point at a region of the first silicon oxide layer.
 16. Thesolar cell according to claim 9, wherein a concentration profile ofoxygen in a depth direction from the first conductivity type amorphoussilicon layer to the crystalline silicon substrate has a maximum pointat a region of the first silicon oxide layer.
 17. A solar cell modulecomprising: a plurality of solar cells according to claim 9, which istwo-dimensionally arranged; a front surface protective member disposedon a front surface side of the plurality of solar cells; a back surfaceprotective member disposed on a back surface side of the plurality ofsolar cells; a front surface encapsulant member disposed between theplurality of solar cells and the front surface protective member; and aback surface encapsulant member disposed between the plurality of solarcells and the back surface protective member.
 18. A solar cellcomprising: a crystalline silicon substrate; a first silicon oxide layerdisposed on a back surface of the crystalline silicon substrate andincluding phosphorus as an impurity; a first dielectric layer disposedon the first silicon oxide layer; and a first conductivity typeamorphous silicon layer disposed on the first dielectric layer andincluding a p-type dopant.
 19. The solar cell according to claim 18,wherein the first dielectric layer comprises a first intrinsicdielectric layer being substantially intrinsic.
 20. The solar cellaccording to claim 18, wherein the first dielectric layer comprises oneof a silicon oxide layer, a silicon nitride layer, and an aluminum oxidelayer.
 21. The solar cell according to claim 18, wherein the firstconductivity type amorphous silicon layer comprises a microcrystal. 22.The solar cell according to claim 18, wherein the crystalline siliconsubstrate comprises, in the back surface, a diffusion region having aphosphorus concentration higher than that of the crystalline siliconsubstrate.
 23. The solar cell according to claim 22, wherein thephosphorus concentration of the diffusion region is lower than that ofthe first silicon oxide layer.
 24. The solar cell according to claim 18,wherein a concentration profile of phosphorus in a depth direction fromthe first conductivity type amorphous silicon layer to the crystallinesilicon substrate has a maximum point at a region of the first siliconoxide layer.
 25. The solar cell according to claim 18, wherein aconcentration profile of oxygen in a depth direction from the firstconductivity type amorphous silicon layer to the crystalline siliconsubstrate has a maximum point at a region of the first silicon oxidelayer.
 26. A solar cell module comprising: a plurality of solar cellsaccording to claim 18, which is two-dimensionally arranged; a frontsurface protective member disposed on a front surface side of theplurality of solar cells; a back surface protective member disposed on aback surface side of the plurality of solar cells; a front surfaceencapsulant member disposed between the plurality of solar cells and thefront surface protective member; and a back surface encapsulant memberdisposed between the plurality of solar cells and the back surfaceprotective member.